The present invention relates to a pumping arrangement in general, and more particularly to a control arrangement which is to be used in connection with an arrangement for pumping fluids and operative for controlling the output rate thereof.
There are already known various pumping arrangements of the type here under consideration. Usually, such arrangements include one or more pumps which is or are driven by a drive, such as an internal combustion engine. In such pumping arrangements, it is also known to provide an auxiliary pump which discharges control fluid at a rate corresponding to the speed of the drive, a flow restrictor or a throttle being provided in the discharge conduit of the auxiliary pump. It is known from these conventional arrangements that, when the flow restrictor or throttle is of a fixed flow-through cross-sectional area, the pressure in the discharge conduit upstream of the throttle will vary proportionately to the square of the speed of rotation of the auxiliary pump which, in turn, depends on the speed of rotation of the drive. Thus, the pressure in the discharge conduit upstream of the throttle will give an indication of the speed of rotation of the drive. It is also already known from the prior art to utilize the pressurized fluid in the discharge conduit of the auxiliary pump for displacing a control slide or a similar valve between two positions of the same, the control slide being interposed into the control circuit of the respective pump so as to control the fluid flow therethrough in such a manner that, when the pressure in the discharge conduit of the auxiliary pump rises above a predetermined level, the variable-output pump is adjusted toward higher output rates, and conversely when the pressure in the discharge conduit drops below a predetermined value.
In such conventional control arrangements for controlling the output of a variable-output pump, the flow-through cross-sectional area of the throttle, which is determinative of the pressure with which the control fluid in the discharge conduit of the auxiliary pump acts on the control slide, and the force exerted on the control slide by a spring which urges the control slide against the action of the pressurized control fluid, are so selected relative to one another that, when the speed of rotation of the drive decreases by a certain amount with respect to a predetermined operating value, the force of the spring overcomes the force exerted by the pressurized fluid in the discharge conduit on the control slide, and the latter is displaced into a position in which the output of the variable-output pump is decreased. One of the main disadvantages of these prior-art constructions is the fact that, in general, the adjustment of the output rate of the variable-output pump proceeds rather rapidly when compared to the rate at which the speed of rotation of the drive changes, so that there exists a danger that the control arrangement for the pumping arrangement may have a high degree of instability due to the likelihood that the control arrangement will so control the output rate of the pumping arrangement that the latter will overshoot or undershoot the proper values of the output rates which correspond to the proper loading of the drive.